1. Field of the Invention
The present invention generally relates to manufacturing methods of coordinate position detecting devices.
2. Description of the Related Art
A touch panel, for example, has been used as an input device of a computer system. The touch panel is provided on a display and configured to detect a coordinate position on the display and obtain a detection signal corresponding to the coordinate position. A direct input can be performed on the touch panel so that the input can be performed easily and intuitively.
Various types such as a resistive film type, an optical type, and a capacitive coupling type have been suggested for the touch panel. It is a general practice to use the resistive film type having a simple structure and a simple control system for the touch panel. There are 4-wire type, 5-wire type, 8-wire type, and other low resistive touch panels, depending on the arrangement of electrodes on the resistive film.
In the 5-wire type resistive film touch panel compared to the 4-wire type or 8-wire type resistive film touch panel, a conductive film of an upper part board arranged at an operating surface side is exclusively for electric potential reading. Accordingly, the 5-wire type touch panel does not have a problem of an edge sliding, which is one of problems of the 4-wire type or 8-wire type resistive film touch panel. Because of this, the 5-wire type touch panel has been used in hard service conditions or in a case where a long endurance term is demanded.
FIG. 1 is a view showing a structure of a 5-wire resistive film touch panel.
A 5-wire resistive film touch panel 1 shown in FIG. 1 includes an upper part board 11 and a lower part board 12. A transparent resistive film 22 is formed on the entire surface of a glass substrate 21 of the lower part board 12. X-axis coordinate detection electrodes 23 and 24 and Y-axis coordinate detection electrodes 25 and 26 are formed on the transparent resistive film 22.
A transparent resistive film 32 is formed on a film board 31 of the upper part board 11. A coordinate detection electrode 33 is formed on the transparent resistive film 32.
First, by applying voltages to the X-axis coordinate detection electrodes 23 and 24, an electric potential distribution is generated in an X-axial direction of the transparent resistive film 22 of lower part board 12. At this time, the electric potential of the transparent resistive film 22 of the lower part board 12 is detected so that an X coordinate of a position where the upper part board 11 comes in contact with the lower part board 12 can be detected.
Next, by applying voltages to the Y-axis coordinate detection electrodes 25 and 26, an electric potential distribution is generated in a Y-axial direction of the transparent resistive film 22 of the lower part board 12. At this time, electric potential of the transparent resistive film 22 of lower part board 12 is detected so that a Y coordinate of the position where the upper part board 11 comes in contact with the lower part board 12 can be detected.
In the above-mentioned touch panel, there is a problem in generating the electric potential distribution uniformly on the transparent resistive film 22 of lower part board 12. In order to make the electric potential distribution on the transparent resistive film 22 of lower part board 12 uniform, for example, a method where electric potential distribution correction patterns are provided in the periphery at plural stages is disclosed in Japanese Laid-Open Patent Application No. 10-83251.
In addition, a method where a common electrode is provided so as to surround the perimeter of an input screen is disclosed in Japanese Laid-Open Patent Application No. 2001-125724.
Furthermore, a method where an opening part is provided at an insulation film formed on a transparent resistive film and an electric potential is supplied from the opening part is disclosed in Japanese Laid-Open Patent Application No. 2007-25904.
A coordinate input device has been required to have a narrow frame due to miniaturization of the apparatus where the coordinate input device is provided.
However, in a coordinate input device described in Japanese Laid-Open Patent Application No. 10-83251, it is necessary to provide the electric potential distribution patterns in the periphery at plural states. Hence, it is difficult to make the frame of the coordinate input device narrow.
Furthermore, in the method described in Japanese Laid-Open Patent Application No. 2001-125724 where the common electrode is provided so as to surround the perimeter of the input screen, if the resistance ratio of the transparent resistive film and the pattern resistance is not large, the electric potential distribution of the transparent resistive film is not uniform.
In addition, in the method described in Japanese Laid-Open Patent Application No. 2007-25904 where the opening part is provided at the insulation film, while the above-mentioned two problems may be solved, the manufacturing process may be complex. Hence, due to non-uniformity of a value of resistance of a material or upon manufacturing, the yield of products with good properties may be degraded.